Stented bioprosthetic valves -- that is, supported valvular grafts which may be either xenografts (heterografts) or allografts (homografts) -- are believed to have important clinical advantages over mechanical non-tissue prosthetic valves. Reports on the use of xenograft valves indicate that the risks of thromboembolism are lower, the need for long-term anticoagulation is minimized, and the nature of ocassional valve failure is progressive, thereby permitting elective reoperation under optimal conditions. Carpentier et al, J. Thorac. Cardiovasc. Surg. 68:771 (1974); Zuhdi et al, Ann. Thorac. Surg. 17:479 (1974); Horowitz et al, J. Thorac. Cardiovasc. Surg. 67:885 (1974).
In general, such grafts have been mounted on supporting frames which provide rigid orifice rings (see U.S. Pat. Nos. 3,570,014, 3,755,823; Weldon et al J. Surg. Research 6:548 (1966)), even though some stents have included struts capable of flexing inwardly to a limited extent, thereby reducing stresses imposed on the grafts during valve operation and decreasing possible erosion of surrounding tissues of the patient (see Sugie et al, J. Thorac. Cardiovasc. Surg. 57:455 (1969); Hardy, Human Organ Support and Replacement, 338 et. seq. (Thomas, 1971); U.S. Pat. No. 3,755,823). Despite encouraging results in the use of stented valvular grafts, and the significant advantages of bioprosthetic heart valves in contrast to totally artificial prosthetic valves, there is a continuing need for improvement, particularly with regard to the long range durability and reliability of the supported valvular grafts.